Gravity meter



April 13, 1954 s. P. WORDEN GRAVITY METER Filed Dec. 8, 1947 FIG. 2

. INVENTOR.

ATTORNEYS Patented Apr. 13, 1954 OFFICE GRAVITY METER Samuel P. Worden,

Texas Instruments` Houston, Tex., assignor to Incorporated, Dallas,Tex.,

a corporation of Delaware Application December 8, 1947, Serial No.790,346

(Cl. i3- 3,821

12 Claims.

This invention relates to a gravity meter.

While the invention herein described has been specically shown asapplied to a gravity meter the principle of the invention is alsoapplicable to force measuring instruments, force controllinginstruments, surveying instruments, geophysical instruments and otherinstruments which require compensating mechanism to neutralizetemperature changes or other physical variations suchA as barometric orhumidity nuctuations however, the invention relates more specically togravity actuated instruments that are used in observing. subsurfaceformations for the location of oil or other minerals.

An object of the invention is to provide an instrument of the characterdescribed which will accurately indicate changes in gravity and therebyascertain the location of valuable subterranean mineral deposits; and.while the instrument herein disclosed embodies certain principlescommonly employed in meters in common use it also comprehends certainimprovements which allowsvsuch meters to be operated and used withoutthermostatic control.

Another object of the invention is toprovide t an instrument of thecharacter described which is of very simple construction and which, atthe same time, willpermit very` delicate measurements and is smaller insize and ofv less weight and more rugged than conventional types ofgravity meters now in use.

A further object of the invention is. to pro-vide an instrument of thecharacter described embodying a compensating device which dispenses withthe necessity of a thermostatic control.

A still further feature of the invention resides ,in the provision of aninstrument of the character described which is of such construction andsize that the working parts may be more efliciently insulated.

Other objects and advantages will be apparent from the followingspecification which is illustrated by the accompanying drawings,wherein:

Figure 1 is an enlarged, fragmentary, vertical sectional view showingone form of the instrument in perspective.

Figure 2 is a vertical, sectional view. of, the instrument of the typeshown in Figurel l.

Figure 3 is an enlarged, perspective detail of the temperaturecompensator shown in Figure 1 Figure 4 is another embodiment of thetemperature compensator.

Ejigure 5 is an elevational view, part1y^ I,1-Se,Q-. tion, of anotherembodiment of the readingfdevice, and

Figure 6 is an enlarged, sectional view of a microscope tube employed.

Referring now more particularly to the drawings'wherein like numerals ofreference designate the same parts in each of thegures, the numeral ldesignates the outer housing of the instrument. The housing may beof anyselected shape and composed of any suitablematerial.

Suspended within the housing from the top or lid thereof, there is anevacuated iiask 2 which is spaced from the housing. all the way aroundand is preferably formed throughout of double walls spaced apart andwhich serves to provide thermal insulation for the mechanism within theinner case 3. This inner casev is within, and spaced from, the flask andis suspended from the lid or cover of the outer housing l by means of a.tube 4 of thermal insulating material and also preferably filled withinsulation.

The inner case 3 yis preferably formed of metal having high thermalconductivity, such as copper, and this inner caseV should behermetically sealed to excludemoisture and dust and to avoid variationsin humidity, temperature and barometric pressure.

Mounted in the, top or lid of the housingv l and extended also throughthe top of, and into, the inner case 3 thereis a microscope tube 5lprovided with any selected number and kind of lenses as 5a, 5b. It alsohas a crosshair t at a selected location.

Also mounted in the top of the. housing I there is a light tube 'l whichextendsondown through the top of, and into, the inner case 3. The lowerend 'la of the tube` l is turned horizontally with its free end upturned underneath the lower end of the microscopev tube 5. The upperend of the light tube is c losed and in said tube there isa source oflight, preferably an electric light 8 connected with the electricwiringe. The wiring may be connected witha battery, preferably carriedby the instrument. Also within the light tube are reiiectors such as lil and l I arranged so as to reflect the light through the upturned endof saidtube.v

I heinclusiony of the temperature compensating device,A hereinafter morespecifically described, dispenses with the necessity of aheavy storagetype battery. This greatly reduces the, size and v /eight of theinstrument herein described, thus also rendering it more portable,Conventional gravity metersv now commonly used weigh from nity toseventy-fivepounds. whereas the meter embodying thepresentcinventionwill weigh appreaimatelyve pounds..

Depending from the top of the inner case 3 there is a rod I2 having thelower overturned end I3 which extends horizontally when the instrumentis in operative position and extending outwardly from said overturnedend I3 there are the supporting rods lo and l5 in parallel relationshipand spaced apart. Upstanding from the rod lll are the spaced arms I6, i8and upstanding from the rod I5 are the spaced arms II, I'I. Rod I2should be of material of low thermal expansion.

Between the upper ends oi the arms I6 there is a spindle I8 Whose endsare connected to the upper ends of the arms i6 by the pivots i9, I9. Thespindle I8 may be mounted on the upstand.- ing arms i5 in any otherpreferred manner so that it will freely rotate about its longitudinalaxis.

Fixed to and upstanding from the spindle i8 there is a rod 2@ whoseupper end is overturned across the upturned end of the tube 'I thusforming a pointer 2I which cci-operates with the cross hair E in amanner hereinafter stated.

Extending out horizontally from the spindle I8 there is an arm 22 Whoseiree end carries a Weight 23. The arm 22 Works through a verticallyelongated eye 2t formed on the outer end of the supporting rod 25 which,in turn, is fixed to the overturned end I3 of the rod I2.

Between the upper ends of the upstanding arms I`I, I'i there is aspindle 26 whose ends may be connected to the upper ends of said arms bymeans of the torsion ties 21, 21. However, the spindle may be mounted onthe arms il in any other preferred manner so as to rotate on alongitudinal axis. The spindles I8, 26 have the arms 28 and 29,respectively, fixed thereto and extending toward each other the formerbeing located beneath the latter and the free ends of these arms areiconnected by means of the mass supporting spring 30. Secured to theunderside of the top of the case 3 are the flexible anchors 3l and 32and secured to one end of the spindle 28 there is a cross-arm 33. Theanchor 3i is connected to one end of the cross-arm 33 by means of arelatively weak pull spring 3 and the anchor 32 is connected to theother end of said cross-arm by a pull spring 35.

An elastic system is thus provided which is supported by the rod i2. Thearm 22 extends hori- Zontally and is constrained in its verticalmovement by the eye 24. rThe pointer 2i and the arm 28 also contributesome mass to the elastic system. The lcenter of gravity oi the entiresuspended system is on a horizontal plane passing through the axes ofthe spindles I8, 26.

A novel feature of the instrument herein described resides in the factthat the helical spring 30 which supports the mass, or weight, 23 isessentially in a vertical position and is attached to said mass, orweight, at a point in a vertical plane parallel to the axis of thespindle I8 and passing through the center of gravity of the entiresuspended system.

To achieve proper sensitivity the tension spring 30 is attached at apoint such that a line from the point through the axis of the spindle I8forms an angle of approximately forty-iive degrees with the horizontalplane through said axis of the spindle I8. This arrangement reducesstress on the pivots IS, I9 and also the stress on the spring 3U. Ascompared to other positions of a similar spring as used in otherinstruments of this type this position of the tension spring` 30relieves the elastic system of undesirably high stresses which result ininaccuracies of operation.

Means for nulling the instrument has been provided. This may beaccomplished by moving the upper end of the tension spring 30 by meansof the arm 29 so as to change the angle of the application of its force.

Force causing said adjusting or nulling motion of the arm 29 is appliedby the springs 3c, 35.

Heretofore temperature compensating systems for such instruments havebeen made and adjusted to correct for temperature changes in a limitedrange only, the correction becoming less accurate at both higher andlower temperatures. In this present invention the adjustable andcontrollable motion of the compensator arm 29 is obtained by a noveldesign by including a short extension spring 3B in one member 35o of thedifferential expansion structure. This spring is short and non-linear,its extension being disproportional to the force acting upon it.

As best seen in Fig. 3, the temperature compensating structure consistsof a pair of arms 29 and Sb joined at their extending ends and connectedby a spacing arm 3T at their other ends. These arms are made of suitablemate rials having different coefficients of thermal expansion. It willbe apparent to those skilled in the art that a change in temperaturewill cause the relative lengths oi' the arms to change thus creating aforce tending to bend or move one or both of the arms 29 and 36D therebymoving the extending ends of the arms 29 and 36h generally in an arcalbout the spindle 26. In a preferred form the supporting spring 30 iscorrnected directly to the extending ends of arms 29 and 36o, the abovedescribed movement of the compensating structure moving the end or thespring 30 to which it is connected in such a Way as to effectivelycompensate for the effect of temperature variations on the system.

Such a structure can be adjusted to provide the necessary compensatingmovement through only a very limited temperature range, and bel yondthis range the compensating movement becomes too large or too small dueto the inherent non-linearity of the system. This difficulty is overcomein the present invention by the addition of a short non-linear springindicated by the reference numeral 3B to an arm of the temperaturecompensating structure. This spring 36 yields non-linearly to the forceproduced by the differential expansion in the connected arms 29 and 36oresulting in a controlled compensating movement of the extending endover a large temperature range. rI'hose skilled in the art can adjustthe non-linearity of spring 35 to provide the desired compensatingmovement.

It is understood that a non-linear spring 36 may be connected at anysuitable part of the system and need not be attached directly to eitherof the compensating arms 29 or 35h.

An alternative form is shown in Fig. 4 wherein a linear spring 36o isconnected to the compensating structure through a spacing arm 3S securedto the spindle 2t and to the extending end of the arms 29a and 36a by anarm 38. It can be seen that the movement of the extending end of thetemperature compensating structure due to deections of arms 29a and 3613by temperature variations will result in a non-linear change of themoment about the spindle 26 exerted by the spring 36e on the extendingend of the temperature compensating structure. Those skilled in the artcan adjust the non-linearity of the changeiof moment.l` to obtain :the.desiredamove-'I ment ofthe fextend-ing'fendlof the arms 29m-'36a and38-.l.l"flfhus,.a vlinear spring may.' be Vuseduto provide-theidesiredunon-'linean .force to correct' the fcompensatingiaction of thetemperature compensatirngv structure. .Other...than. these: changes. ithe "temperature 'compensatingstructuresillus-v the .temperaturecompensating mechanism. such as s 1 own inFigurei3 'or Figure .41themotion im-f partedtby the .temperature compensation. mechanismt totheiendlof. the :spring isthat. mo-'J tion required foric'ompensating.the resultant ef.:-

feet'of temperature; changes. on .all partsfof the. .1-1; system.throughout La:` reasonably-wide' working.

rangen.

Attention is called :to the factthat .it is not necessary that `.the'labilized compensator be connecteddirectly'or indirectly'to thesupporting spring' 'as indicated in the preferred .design shown inFigure' 11. The labilized compensator maysact' directlyon the mass 23,thus changing its distance from -the 'sfulcrum *andcorrespondinglyiichanging its moment-1 1..It may .also act upon'the mass.fas an additional lifting forc'e similar.y to, butfindependentl of,`the :supporting spring..f

In Figure 5 va modification is illustrated wherein themicroscopetubeii.is not employed. A light tube. 'Ib isextendeddownwardly through the top of the housing l/andfinto the vinnercase 3 in verticalalignmentover the spindle i8. The upperendof'thelight'tubelb isclosed and is provided: with a'. light Vinlet side'opening 4U. l' In front of this-opening .there :is mounteda suitablevlens '4l anda source of light'42. The rays of lightfrom'said'sourcefpassithrou h the lens andthrough saidf'opening andaredeflected vdownwardly by the deflector 43 withinthe tube' 1b. Mountedvon theispindle .I8 there. is an upwardlydirected` mirrorril'll whoseupper surfacer is preferably concave.' The downwardly deilectedrrays oflight are reectedby the-mirror onto an inside deiiector 45 and-outthrough the tuberll thus forminganirnage-of the-crosshair- 41 on asuitable lens 48.

Fitted downwardlythrough thelid, or cover, of the outer housing thereare the adjustingY rods 49 and 50 whose lower-ends are threadedIthroughthe Atopof the inner case Sand bear against the respectiveflexible' anchors '3l and 32. These `anchors have suiiici'entilexibility' to maintain the springs 3a, 35 undera predeterminedVtension .but this tensionmay be reduced in either spring `by screwingthe .correspondingl rod 49 or 50 downwardly to ex the correspondinganchor downwardly.

In use the instrument may be set at a selected locationand brought to alevel by properly adjusting the feet 5I on which the instrument ismounted.' There `are preferably three of these feet' but only twoareshowniin Figure 2; When the instrument is brought `to a level this willbe indicated by a spirit level 52 on the instrument. The gravitationaleiec't of the mass may move the pointer 2| so as to cast a: shadoweccentric withv respect to the crosshair S. Thereupon vthe rod V49 maybe turned to changethe tension on the spring'34 and to bringthe shadowcastby the pointer 2i into .registrationwith the crosshair :6.: Onthe'iheadtof the rod 49 thereis a dial153 4andathere ai.v co-operating..upstanding L pointer 54 on .the V.top fof .thev instrument whereby the"lgravitationalazforce on the :.imass223 mayrbe .ifregisteredf.:iThezinstrument.may then be moved.y to another location.and theprocess repeated and. 1

the diierencesi, .if anyyfof thegravitational force of thetwoilocationsthusindicated. If the form:

these'..zvariations maybe registered by the turning of the dial "53. inthe manner hereinabove indicatedii Thev drawings. and :descriptionillustrate what is now. .considered to be preferred forms of theinvention by way of illustration only while the broadiprinciple oftheinvention will be dened by the :appended claims: What :I folaim is: l. Agravity-measuring device comprising; an

elastic system including'a mass, a movable support, yieldable meanssuspending the mass from thersupport, and meansfor adiustably movingsaidisupport for restoring the mass to a null position; and.atemperature-compensating structurek comprising two generally parallelmembers of diierent thermal expansion joined at spaced points adjacenttheir ends, one .of said members including means which imparts thereto anonlinear `resiliencyv along an axis connecting said spaced pointswhereby temperature variations effect va nonlinear relative lateralmovement to said. ends,` one end of the temperature-compensatingstructureconnected to the movable support and the other end linked tothe yieldable means, the temperature-responsive lateral movement of theother end'being adjusted in amplitude and linearity and having a`component in the direction of action of the yieldable means forcompensating for temperature variations.

2. A gravity-measuringdevice comprising; an elastic system vincludingafznass, a movable support, yieldablefmeans .suspending the mass fromthe support,..and .means for adjustably moving said. supportl forrestoringithe mass to a null position; anda temperature-compensatingstructure comprising two generally parallel members of differentthermal-expansion joined' at spaced points adjacent their ends, one ofsaid members including means-which: imparts thereto a nonlinearresiliency .along an axis yconnecting said spaced points wherebytemperature variations effeet a nonlinear relative lateral movement tosaid ends, onexend of the temperature-compensating structure connected.nto the movable support and the other linkedV to the mass, thetemperatureresponsive-'lateral movement ci the other endbeingadjusted'in amplitude `and linearity and having-a componenttinthedirection of action of theyieldable meansffor compensating forteinperature variations" 3. A' gravity-measuring device comprising; anelastic system including a mass, a iixed support,

yieldable meanssuspending the mass, means tions effectanonlinearrelative lateral movement` to saidendsfone end-of thetemperature-compensating structure connected to the xed support and theother end linked to the yieldable means, the temperature-responsivelateral movement of the other end being adjusted in amplitude andlinearity and having a component in the direction of action or theyieldable means for compensating for temperature variations.

Li. A gravity-measuring device comprising; an elastic system including amass, a fixed support, yieldable means suspending the mass, and meanslinked to the yieldable means for adjustably moving` the yieldable meansfor restoring the mass to a null position; and atemperature-compensating structure comprising two generally parallelmembers or cliiierent thermal expansion joined at spaced points adjacenttheir ends, one of said members including means which imparts thereto anonlinear resiliency along an axis connecting said spaced points wherebytemperature variations enect a nonlinear relative lateral movement tosaid ends, one end of said temperaturecompensating structure connectedto the fixed support and the other end linked to the mass, thetemperature-responsive lateral movement of the other end being adjustedin amplitude and linearity and having a component in the direction ofaction of the yieldable means for compensating for temperaturevariations.

5. A gravity-measuring device comprising, a mass, a support rotatableabout its longitudinal axis, a spring suspending the mass from thesupport, adjustment screws for adjustably moving said support forrestoring the mass to a null position, and a temperature-compensatingstructure comprising two generally parallel members or different thermalexpansion joined at spaced points adjacent their ends, one of Saidmembers including a nonlinear spring which imparts thereto a nonlinearresiliency along an axis connecting said spaced points wherebytemperature variations eect a nonlinear relative lateral movement tosaid ends, one of said ends connected to the movable support and theother end connected to and supporting the spring, thetemperatureresponsive lateral movement of t -e other end being adjustedin amplitude and linearity and having a component in the direction ofaction of the spring for compensating for temperature variations Si Agravity-measuring instrument comprising, an elastic system including amass, a support rotatable about its longitudinal axis, an elastic memberresiliently supporting the mass from the support, the elastic memberbeing a zero-length helical spring, and means for adjustably moving thesupport for restoring the mass to a null position, and atemperature-compensating structure comprising two generally parallelmembers of different thermal expansion joined at spaced points adjacenttheir ends, one of said members including means which imparts thereto anonlinear resiliency along an axis connecting said spaced points wherebytemperature variations eiect a nonlinear relative lateral movement tosaid ends, one end of the temperaturecompensating structure connected tothe movable support and the other end attached to and supporting thezero-length helical spring, the points of attachment of the spring tothe temperature-compensating structure and to the mass beingsubstantially in a vertical plane, the tempeinture-responsive lateralmovement of the other end being adjusted in amplitude and linearity andhaving a component in the direc-- tion of action of the zero-lengthhelical spring for compensating for temperature variations.

7. A gravity-measuring device comprising, a. mass, a spring supportingsaid mass, a spindle rotatable about a horizontal axis, a iirstresilient beam extending radially from the spindle, said spring havingits upper end attached to and supported by the extending end of saidbeam, means for adjustably lrotating the spindle for restoring the massto a null position, and a second beam of dierent thermal expansion fromsaid iirst beam and joined to the said first adjacent their ends, saidrst and second beams being disposed in generally parallel relation, saidsecond beam including means which imparts to said iirst and second beamsa nonlinear resiliency along an axis connecting said spaced pointswhereby temperature variations eiect a nonlinear relative lateralmovement to said ends, said temperature-responsive movement beingadjusted in amplitude and linearity and having a cornponent in thedirection of action of the spring for compensating for temperaturevariations.

8. In a gravity-measuring device, an elastic system comprising, a firstspindle rotatable about a horizontal axis, a first arm extendingupwardly from said rst spindle at an angle or about fortyfive degrees toa horizontal plane passing through the axis of said first spindle, asecond spindle rotatable about a horizontal axis, a second arm extendingdownwardly from said second spindle and towards said nrst arm and at anangle of about forty-five degrees to a horizontal plane passing throughthe axis of the second spindle, such iirst and second arms being in thesame vertical plane and having their extending ends in substantiallyvertical alignment, a spring in an approximately vertical position whoseupper and lower end-.s are connected to the extending ends of said arms,a weight member adapted to respond to the force to `be measured, a thirdarm connecting the weight member to the second spindle, and meansconnected to the iirst spindle for adjustably rotating the first spindlefor restoring the weight member to a null position.

9. The gravity-measuring device of claim 8 where the rst arm isresilient and which includes a fourth arm of -dierent thermal expansionfrom the iirst arm connected in generally parallel relation at spacedpoints to the rst arm adjacent their ends, one of said iirst or fourtharmsJ including means which imparts thereto a nonlinear resiliency alongan axis connecting said spaced points whereby temperature variationseffeet a nonlinear relative lateral movement to the said iirst andfourth arms, said temperatureresponsive lateral movement being adjustedin amplitude and linearity and having a component in the direction ofaction of the spring or'compensating for temperature variations.

10. A gravity-measuring device comprising; an elastic system including amass, a spindle rotatable about a horizontal axis, yieldable meanssuspending the mass from the spindle, second yieldably means connectedto said spindle for adjustably rotating the spindle for restoring themass to a null position; and a temperature-compensating structurecomprising a resilient arm extending radially from the spindle andconnected to an upper end of and supporting the yieldable means, anonlinear spring connected at spaced points to and adjacent the ends ofthe resilient arm, said arm and springbeing disposed in generallyparallel relation and being of different thermal expansion,` saidnonlinear spring imparting to the rebeam at spaced points' silient arm anonlinear resiliency along an axis connecting said spaced points wherebytemperature variations effect a nonlinear relative lateral movement tosaid ends, the temperature-responsive lateral movement of the ends beingadjusted in amplitude and linearity and having a cornponent in thedirection of action of the yieldable means for compensating fortemperature variations.

11. A measuring device comprising, a mass, a movable support, yieldablemeans suspending the mass from the support, and means for adjustablymoving said support for restoring the mass to a null position, and atemperature-compensating structure comprising a resilient arm extendingradially from the movable support and joined at its extending end to andsupporting the yieldable means, and a nonlinear spring joined at spacedpoints to and adjacent the ends of the arm, said arm and spring beingdisposed in generally parallel relationship and being of diierentthermal expansion, said nonlinear spring imparting to thetemperature-compensating structure a nonlinear resiliency along an axisconnecting said spaced points whereby temperature variations eect anonlinear lateral movement to said ends, the teinperature-responsivelateral movement of the eX- tending end being adjusted in amplitude andlinearity and having a component in the direction of action of theyieldable means for compensating for temperature variations.

12. A measuring device comprising, a mass, a movable support, yieldablemeans suspending the yconnecting the spaced points mass from thesupport, and means for adjustably moving the support for restoring themass to a null position, and a temperature-compensating structurecomprising a rst arm extending radially from the movable support andjoined at its extending end and supporting the yieldable element, asecond arm joined at spaced points to said first arm adjacent theirends, and a third arm having a linear spring joined at spaced points tosaid rst arm adjacent their ends, such arms being of different thermalexpansion and being disposed in generally parallel relation, said linearspring imparting a nonlinear resiliency along an axis of said armswhereby temperature variations effect a nonlinear relative lateralmovement of said ends, the temperature-responsive lateral movement ofthe extending end of the rst arm being adjusted in amplitude andlinearity and having a componentI in the direction of action of theyieldablemeans for compensating for temperature variations.

References Cited in the file of this patent UNITED STATES PATENTS

